Transmission and vehicle having transversely mounted transmission and engine arranged in axial direction thereof

ABSTRACT

A vehicle includes an engine, a pair of side frames extending along a vehicle body, and a transmission adapted to be axially connected with the engine and transversely mounted on the vehicle body, including, an input shaft, an output shaft, a first counter shaft, a second counter shaft, a reverse shaft, a first gear mechanism, a second gear mechanism, a third gear mechanism, a reverse movement gear mechanism and a transmission case, wherein the first and second gear mechanisms are arranged relatively close to the engine, the third gear mechanism is arranged more remote from the engine than the second gear mechanism, the transmission case includes a back wall portion having a first back wall portion, a second back wall portion and a third back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2007-235833, filed on Sep. 11, 2007, the entire contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a vehicle having an engine and a transmission that are connected to each other in an axial direction thereof and that are transversely mounted on the vehicle relative to a vehicle body.

BACKGROUND

In order to downsize a transmission and increase output torque, for example, a transmission apparatus disclosed in JP2002-70960A, adapted to a front-engine front-drive type vehicle to which an engine connected in an axial direction thereof are transversely mounted, includes an input shaft, two counter shafts and plural shift stage gear sets that are arranged in parallel to each other between the input shaft and each of the counter shafts, thereby shortening length of the transmission apparatus in an axial direction thereof without reducing number of shift stages. A transmission 1 illustrated in FIG. 4 has substantially the same structure as the transmission apparatus disclosed in the second embodiment of JP2002-70960A. As illustrated in FIG. 4, an input shaft 3 a, first counter shaft 3 b, a second counter shaft 3 c and a reverse shaft 3 d are arranged in parallel to each other within a transmission case 2. The first counter shaft 3 b and the second counter shaft 3 c are connected to output shafts 8 a and 8 b via reduction gear set 6 a, 6 b and 6 c and a differential mechanism 7. A first forward movement gear switching unit 4A forming a 1st shift stage and a 2nd shift stage and a second forward movement gear switching unit 4B forming a 3rd shift stage and a 4th shift stage are arranged between the input shaft 3 a and the first counter shaft 3 b so that the second forward movement gear switching unit 4B is positioned farther away from an engine 10 than the first forward movement switching unit 4A. A third forward movement switching unit 4C forming a 5th shift stage and a 6th shift stage is arranged between the input shaft 3 a and the second counter shaft 3 c so as to be located at a position substantially corresponding to the position where the second forward movement gear switching unit 4 a is arranged, in an axial direction of the input shaft 3 a. Further, a reverse movement gear switching mechanism 4D forming a reverse shift stage is arranged between the input shaft 3 a, the second counter shaft 3 c and the reverse shaft 3 d so as to be located at a position substantially corresponding to the position where the first forward movement gear switching unit 4A is provided, in the axial direction of the input shaft 3 a. A back wall portion 2 a of the transmission case 2, substantially corresponding to an area where input shaft 3 a, the first counter shaft 3 b and the second counter shaft 3 c are arranged orthogonally relative to the back wall portion 2 a, is formed to have a flat surface.

FIG. 5 schematically illustrates a forward portion of the vehicle, viewed in a lateral direction thereof, to which a driving unit is transversely mounted at the forward portion of a vehicle body. The driving unit is a unit in which the transmission 1 disclosed in JP2002-70960A is connected to the engine 10 in an axial direction thereof. As illustrated in FIG. 5, the driving unit is positioned between a pair of side frames 9 extending along both sides of the vehicle body in a front-rear direction thereof. In order to prevent the side frames 9 from interfering with a front axle, forward portions of the side frames 9 are curved upwardly. Hence, as illustrated in FIG. 6, the side frame 9 at the left side in FIG. 5 extends along immediate left of an upper portion of the back wall portion 2 a of the transmission case 2 in the front-rear direction of the vehicle.

In order to increase collision safety and vehicle stiffness, a cross-section of each of the side frames 9 needs to be enlarged and a shape of each of the side frames 9 needs to be linearized. The side frames 9 a having the enlarged cross-sectional area and the linearized shape are illustrated with chain double-dashed lines in FIG. 5. As is evident from the position of the side frames 9 a having the enlarged cross-section and illustrated with the chain double-dashed lines in FIG. 5, the side frame 9 a at the left side in FIG. 5 interferes with an upper left portion of the back wall portion 2 a of the transmission case 2, and the side frame 9 a at the right side in FIG. 5 is positioned closer to the engine 10. Hence, the driving unit having axially connected engine 10 and transmission 1 may have difficulties when being transversely mounted on the vehicle body. A case where the driving unit, in which the engine and the transmission are connected in the axial direction thereof, is adapted to the front-engine front-drive type vehicle is described above. However, as is the case with the transmission adapted to the front-engine front-drive type vehicle described above, in a case where a similar driving unit is adapted to a rear-engine rear-drive type vehicle, the driving unit in which the transmission 1 and the engine 10 connected in the axial direction thereof may have difficulties when being transversely mounted on the vehicle body because of the similar reasons explained above.

The transmission apparatus disclosed in JP2002-70960A suggests a modified transmission apparatus in which a portion of the back wall of the transmission case positionally corresponding to the second counter shaft is arranged closer to the engine, compared to a portion of the back wall positionally corresponding to the first counter shaft, by eliminating one shift stage. However, in the transmission apparatus disclosed in JP2002-70960A, the portion on the back wall, corresponding to the second counter shaft and positioned closer to the engine than other portions of the back wall, is positioned at lower portion of the transmission case, thus resulting in creating a dead space at the back wall portion of the transmission case. Hence, even with the modified transmission apparatus disclosed in JP2002-70960A, the driving unit may have difficulties when being transversely mounted on the vehicle.

A need thus exists for a vehicle which is not susceptible to the drawback mentioned above.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a vehicle includes an engine, a pair of side frames provided at the vehicle so as to extend along both sides of a vehicle body in a front-rear direction of the vehicle, and a transmission adapted to be axially connected with the engine and adapted to be transversely mounted on the vehicle body, including an input shaft adapted to be rotatably driven by the engine, an output shaft adapted to be connected to driving wheels, a first counter shaft arranged in parallel to the input shaft and connected to the output shaft, a second counter shaft arranged in parallel to the input shaft and connected to the output shaft, a reverse shaft arranged in parallel to the input shaft and connected to the output shaft, a first gear mechanism between the input shaft and the first counter shaft, the first gear mechanism having a first gear set, a second gear set and a first switching clutch therebetween to selectively establish power transmission paths between the input shaft and the first counter shaft, a second gear mechanism between the input shaft and the second counter shaft, the second gear mechanism having a third gear set, optionally a fourth gear set and a second switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the third gear set or, if present, the fourth gear set, a third gear mechanism between the input shaft and the second counter shaft, the second and third gear mechanisms extending in parallel with one another between the input shaft and the second counter shaft, the third gear mechanism having a fifth gear set, optionally a sixth gear set and a third switching clutch for selectively establishing a power transmission path between the input shaft and the second counter shaft via the fifth gear set or, if present, the sixth gear set, a reverse movement gear mechanism having a reverse gear set provided between the input shaft and the reverse shaft and a reverse movement switching clutch fir selectively establishing a power transmission path between the input shaft and the reverse shaft via the reverse gear set; and a transmission case supporting and covering most of the input shaft, the first counter shaft, the second counter shaft, the reverse shaft, the output shaft, the first gear mechanism, the second gear mechanism, the third gear mechanism and the reverse movement gear mechanism, wherein the first gear mechanism and the second gear mechanism are arranged relatively close to the engine, the third gear mechanism is arranged at a position more remote from the engine than the second gear mechanism, and the first counter shaft is arranged above both the input shaft and the second counter shaft, a driving gear of the second gear set, which is arranged closer to the engine than a driving gear of the first gear set of the first gear mechanism, serves also as a driving gear of the third gear set and is arranged closer to the engine than a driving gear of the fourth gear set of the second gear mechanism, and a driving gear of the first gear set, which is arranged farther from the engine than the driving gear of the second gear set of the first gear mechanism, is positioned on the input shaft substantially aligned with the third switching clutch, in the axial direction of the input shaft, the reverse gear set includes a driving gear provided at the input shaft, a driven gear rotatably supported at the reverse shaft and rotatably connectable to the reverse shaft by means of the reverse movement switching clutch, and an idler gear rotatably supported at the first counter shaft and engaging with the driving gear and the driven gear of the reverse gear set, wherein the driving gear of the reverse gear set serve also as the driving gear for the second gear set, and wherein the transmission case includes a back wall portion formed with a first back wall portion corresponding to the second forward movement gear switching unit and the third forward movement gear switching unit, a second back wall portion corresponding to the first gear mechanism and located closer to the engine than the first back wall portion, and a third back wall portion corresponding to a portion of the reverse movement gear mechanism provided at the reverse shaft and located even closer to the engine than the second back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion.

According to another aspect of the present invention, a transmission adapted to be axially connected with an engine and adapted to be transversely mounted on a vehicle body, includes an input shaft adapted to be rotatably driven by the engine, an output shaft adapted to be connected to driving wheels, a first counter shaft arranged in parallel to the input shaft and connected to the output shaft, a second counter shaft arranged in parallel to the input shaft and connected to the output shaft, a reverse shaft arranged in parallel to the input shaft and connected to the output shaft, a first gear mechanism between the input shaft and the first counter shaft, the first gear mechanism having a first gear set, a second gear set and a first switching clutch therebetween to selectively establish power transmission paths between the input shaft and the first counter shaft, a second gear mechanism between the input shaft and the second counter shaft, the second gear mechanism having a third gear set, optionally a fourth gear set and a second switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the third gear set or, if present, the fourth gear set, a third gear mechanism between the input shaft and the second counter shaft, arranged in parallel to the second gear mechanism in an axial direction of the input shaft, and having a fifth gear set, optionally a sixth gear set and a third switching clutch for selectively establishing a power transmission path between the input shaft and the second counter shaft via the fifth gear set or, if present, the sixth gear set, a reverse movement gear mechanism having a reverse gear set provided between the input shaft and the reverse shaft and a reverse movement switching clutch fir selectively establishing a power transmission path between the input shaft and the reverse shaft via the reverse gear set, and a transmission case supporting and covering most of the input shaft, the first counter shaft, the second counter shaft, the reverse shaft, the output shaft, the first gear mechanism, the second gear mechanism, the third gear mechanism and the reverse movement gear mechanism, wherein the first gear mechanism and the second gear mechanism are arranged relatively close to the engine, the third gear mechanism is arranged at a position more remote from the engine than the second gear mechanism, and the first counter shaft is arranged above both the input shaft and the second counter shaft, a driving gear of the second gear set, which is arranged closer to the engine than a driving gear of the first gear set of the first gear mechanism, serves also as a driving gear of the third gear set and is arranged closer to the engine than a driving gear of the fourth gear set of the second gear mechanism, and a driving gear of the first gear set, which is arranged farther from the engine than the driving gear of the second gear set of the first gear mechanism, is positioned on the input shaft substantially aligned with the third switching clutch, in the axial direction of the input shaft, the reverse gear set includes a driving gear provided at the input shaft, a driven gear rotatably supported at the reverse shaft and rotatably connectable to the reverse shaft by means of the reverse movement switching clutch, and an idler gear rotatably supported at the first counter shaft or the second counter shaft and engaging with the driving gear and the driven gear of the reverse gear set, wherein the driving gear and the driven gear of the reverse gear set serve also as the driving gear for the second gear set, and wherein the transmission case includes a back wall portion formed with a first back wall portion corresponding to the second forward movement gear switching unit and the third forward movement gear switching unit, a second back wall portion corresponding to the first gear mechanism and located closer to the engine than the first back wall portion, and a third back wall portion corresponding to a portion of the reverse movement gear mechanism provided at the reverse shaft and located even closer to the engine than the second back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein:

FIG. 1 is a view schematically illustrating an entire structure of an example of a transmission adapted to a vehicle in which axially connected engine and transmission is transversely mounted;

FIG. 2 is a view schematically illustrating the transmission viewed from the left side in FIG. 1;

FIG. 3 is a view of a portion of the vehicle, viewed in lateral direction thereof, at which the axially connected engine and transmission is transversely mounted;

FIG. 4 is a view schematically illustrating an entire structure of an example of a conventional transmission; and

FIG. 5 is a sectional view of the vehicle, viewed in lateral direction thereof, at which the axially connected engine and the conventional transmission is transversely mounted.

DETAILED DESCRIPTION

An embodiment of a transmission and a vehicle, to which the transmission and an engine connected in an axial direction thereof are transversely mounted, will be described below in accordance with FIGS. 1 to 3 of the attached drawings. FIG. 3 schematically illustrates a sectional view of a forward portion of the vehicle, viewed in lateral direction thereof, in a case where the axially connected engine and transmission of the embodiment is adapted to a front-engine front-drive type vehicle. An engine 10 and a transmission 11, connected with each other in the axial direction thereof, are transversely mounted between forward portions of left and right side frames 13 that serve as primary strength members and that extend along the both side portions of a vehicle body in a front-rear direction of the vehicle. The transmission 11 is arranged at the left of the engine 10 in FIG. 3. A cut-out portion 12 b, which will be described below, is formed at an upper portion of a back wall portion 12 a of a transmission case 12. The forward portion of the left side frame 13 of the left and right side frames 13, whose forward portions are upwardly curved for avoiding interference with a front axle, extends through the cut-out portion 12 b formed at the upper portion of the back wall portion 12 a of the transmission case 12.

As illustrated in FIGS. 1 and 2, the transmission 11 includes an input shaft 15 rotatably driven by the engine 10, an output shaft 19 connected to driving wheels (not shown), first and second counter shafts 16 and 17 and a reverse shaft 18 that are arranged in parallel to the input shaft 15 and that are connected to the output shaft 19 via a reduction gear set 28 a, 28 b, 28 c and 28 d, a first forward movement gear switching unit 20A (a first gear mechanism) arranged between the input shaft 15 and the first counter shaft 16, a second forward movement gear switching unit 20B (a second gear mechanism) and a third forward movement gear switching unit 20C (a third gear mechanism) each of which is arranged between the input shaft 15 and the second counter shaft 17, a reverse movement gear switching unit 20D (a reverse movement gear mechanism) arranged between the input shaft 15 and the reverse shaft 18, and the transmission case 12. The transmission case 12 supports the input shaft 15, the first and second counter shaft 16 and 17, the reverse shaft 18, the output shaft 19, the first, second, and third forward movement gear switching units 20A, 20B, 20C and a reduction gear set 28 a, 28 b, 28 c and 28 d, most of which are accommodated therewithin. The reduction gear set 28 a, 28 b, 28 c and 28 d is arranged at a position which is the closest to the engine 10 among gear sets within the transmission case 12. The first, second and third forward movement gear switching units 20A, 20B and 20C are positioned so as to be more remote from the engine 10 than the reduction gear set 28 a, 28 b, 28 c and 28 d.

As illustrated in FIGS. 1 and 3, the transmission 11 is arranged at one side of the engine 10 so as to be connected therewith in the axial direction of the engine 10. The transmission case 12 is fixed to the engine 10. A left end portion and a middle portion of the input shaft 15 in FIG. 1 is rotatably supported at the transmission case 12, and a right end portion of the input shaft 15 is connected to a crank shaft (not shown) of the engine 10 via a clutch (not shown). Both ends of each of the first counter shaft 16 and the second counter shaft 17 and the reverse shaft 18 are rotatably supported at the transmission case 12. The output shaft 19 is formed with a first shaft 19 a and a second shaft 19 b that are coaxially connected via a differential mechanism 29 arranged within the transmission case 12. The first and second shafts 19 a and 19 b are rotatably supported by the transmission case 12. Further, each outer end portion of each of the first and second shafts 19 a and 19 b is connected to the corresponding driving wheel via a joint and a drive shaft (not shown). The smaller reduction gears 28 a, 28 b and 28 c fixed at the first and second counter shafts 16 and 17 and the reverse shaft 18 respectively engage with the larger reduction gear 28 d, having a larger diameter than the reduction gears 28 a, 28 b and 28 c and provided at the differential mechanism 29, thereby connecting the first and second counter shafts 16 and 17 and the reverse shaft 18 to the output shaft 19. ‘Small’, as used in the reduction small gears 28 a, 28 b and 28 d, does not refer to specific size thereof, but rather because sizes of the reduction gears 28 a, 28 b, and 28 d are smaller than the reduction gear 28 d. Similarly, ‘large’, as used in the reduction large gear 28 d, does not refer to a specific size thereof, but rather because a size of the reduction gear 28 d is larger than other reduction gears 28 a, 28 b and 28 c. Additionally, as illustrated in FIG. 2, the first counter shaft 16 and the reverse shaft 18 are positioned above the input shaft 15 and the second counter shaft 17.

As illustrated in FIG. 1, the first forward movement gear switching unit 20A is arranged at a position relatively close to the engine 10. The first forward movement gear switching unit 20A forms a 1st shift stage and a 2nd shift stage, and includes two pairs of gear sets arranged between the input shaft 15 and the first counter shaft 16, i.e. a 1st shift gear set (first gear set) 21 a, 21 b and a 2nd shift stage gear set (second gear set) 22 a, 22 b, and a first switching clutch 30A. The 1st shift stage gear set includes the driving gear 21 a and the driven gear 21 b, and the 2nd shift stage gear set includes the driving gear 22 a and the driven gear 22 b. The first switching clutch 30A is arranged between the 1st shift stage gear set 21 a, 22 b and the 2nd shift stage gear set 22 a, 22 b, and establishes a power (torque) transmission path established by each of the 1st shift stage gear set 12 a, 22 b and the 2nd shift stage gear set 22 a, 22 b between the input shaft 15 and the first counter shaft 16. The driving gear 21 a of the 1st shift stage gear set 21 and 21 b and the driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b are fixed at the input shaft 15, and the driven gear 21 b of the 1st shift stage gear set 21 a and 21 b and the driven gear 22 b of the 2nd shift stage gear set 22 a and 22 b are rotatably provided at the first counter shaft 16. The first switching clutch 30A is provided between the driven gears 21 b and 22 b, and selectively connects either one of the driven gears 21 b and 22 b with rotation of the first counter shaft 16.

A known synchromesh mechanism is adapted to the first switching clutch 30 A. The first switching clutch 30A incorporates therein a clutch hub L fixed at the first counter shaft 16, a sleeve M spline-engaged with an outer periphery of the clutch hub L so as to be movable in an axial direction of the first counter shaft 16, and engaging members S1 and S2 that are integrally formed at the driven gears 21 b and 22 b, respectively and that are spline-engageable with the sleeve M. When the sleeve M of the first switching clutch 30A is shifted towards the driven gear 21 b by means of a manually or automatically operated shift fork N from a neutral position illustrated in FIG. 1, the sleeve M is spline-engaged with the engaging member S1, and the driven gear 21 b of the 1st shift stage gear set 21 a and 21 b is connected to the rotation of the first counter shaft 16. As a result, the 1st shift stage is established. Further, when the sleeve M is shifted towards the driven gear 22 b by means of the shift fork N from the position where the 1st shift stage is established, firstly the engaging member S1 is disengaged from the sleeve M, and the sleeve M is returned to the neutral position. When the sleeve M is shifted further towards the driven gear 22 b, the sleeve M is spline-engaged with the engaging member S2, and the driven gear 22 b of the 2nd shift stage gear set 22 a and 22 b is connected to the rotation of the first counter shaft 16. As a result, the 2nd shift stage is established. When the sleeve M is shifted towards the driven gear 21 b from the position where the 2nd shift stage is established, the sleeve M is returned to the neutral position.

As is the case with the first forward movement gear switching unit 20A, the second forward movement gear switching unit 20B is arranged at a position relatively close to the engine 10. The third forward movement gear switching unit 20C is arranged at the position more remote from the engine 10 than the second forward movement gear switching unit 20B. The second forward movement gear switching unit 20B forms a 3rd shift stage and a 4th shift stage, and includes a 3rd shift stage gear set (third gear set) 23 a, 23 b and a 4th shift stage gear set (fourth gear set) 24 a, 24 b, both of which are arranged between the input shaft 15 and the second counter shaft 17, and a second switching clutch 30B arranged between the 3rd and second 4th stage gear sets. The 3rd shift stage gear set includes the driving gear 23 a and the driven gear 23 b, and the 4th shift stage gear set includes the driving gear 24 a and the driven gear 25 b. The second forward movement gear switching unit 20B is structured substantially the same as the first forward movement gear switching unit 20A. When a sleeve M of the second switching clutch 30B is shifted towards the driven gear 23 b of the 3rd shift stage gear set 23 a and 23 b from a neutral position illustrated in FIG. 1, the 3rd shift stage is established by the substantially same manner as, for example, the 2nd shift stage is established. When the sleeve M is shifted towards the driven gear 24 b of the 4th shift stage gear set 24 a and 24 b from the position where the 3rd shift stage is established, the sleeve M is returned to the neutral position. When the sleeve M is further shifted towards the driven gear 24 b from the neutral position, the 4th shift stage is established. Further, when the sleeve M is shifted towards the driven gear 23 b from the position where the 4th shift stage is established, the sleeve M is returned to the neutral position.

The third forward movement gear switching unit 20C forms a 5th shift stage and a 6th shift stage, and includes a 5th shift stage gear set (fifth gear set) 25 a, 25 b and a 6th shift stage gear set (sixth gear set) 26 a, 26 b, both of which are arranged between the input shaft 15 and the second counter shaft 17, and a third switching clutch 30C arranged between the 5th and 6th shift stage gear sets. The 5th shift stage gear set includes the driving gear 25 a and the driven gear 25 b, and the 6th shift stage gear set includes the driving gear 26 a and the driven gear 26 b. The third forward movement gear switching unit 20C is structured substantially the same as the first and second forward movement gear switching units 20A and 20B. When a sleeve M of the third switching clutch 30C is shifted towards the driven gear 25 b of the 5th shift stage gear set 25 a and 25 b from a neutral position illustrated in FIG. 1, the 5th shift stage is established by the substantially same manner as, for example, the 1st shift stage is established. When the sleeve M is shifted towards the driven gear 26 b of the 6th shift stage gear set 26 a and 26 b from the position where the 5th shift stage is established, the sleeve M is returned to the neutral position. When the sleeve M is further shifted towards the driven gear 26 b from the neutral position, the 6th shift stage is established. Further, when the sleeve M is shifted towards the driven gear 25 b from the position where the 6th shift stage is established, the sleeve M is returned to the neutral position.

The driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b, arranged at the position relatively close to the engine 10 at the first forward movement gear switching unit 20A, is fixed at the input shaft 15 and serves also as the driving gear 23 a of the 3rd shift stage gear set 23 a and 23 b arranged at the position relatively close to the engine 10 at the second forward movement gear switching unit 20B. The driving gear 21 a of the 1st shift stage gear set 21 a and 21 b, arranged at the position more remote from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b, is fixed at the input shaft 15 at the position substantially corresponding to the third switching clutch 30C of the third forward movement gear switching unit 20C in the axial direction thereof. That is to say, the driving gear 21 a of the 1st shift stage gear set 21 a and 21 b is fixed at the input shaft 15 so as to be arranged between the driving gear 25 a of the 5th shift stage gear set 25 a, 25 b and the driving gear 26 a of the 6th shift stage gear set 26 a, 26 b of the third forward movement gear switching unit 20C.

As illustrated in FIGS. 1 and 2, the reverse movement gear switching unit 20D includes a reverse gear set 27, arranged between the input shaft 15, the first counter shaft 16 and the reverse shaft 18, and a reverse movement switching clutch 30D that is configured to establish a power transmission path established by the reverse gear set 27 between the input shaft 15 and the reverse shaft 18. The reverse gear set 27 is formed with a driving gear 27 a, an idler gear 27 b and a driven gear 27 c. The driving gear 27 a and the idler gear 27 b serve also as respective driving gear 22 a and driven gear 22 b of the 2nd shift stage gear set arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A. Further, the driven gear 27 c is rotatably supported at the reverse shaft 18 and is engaged with the idler gear 27 b (driven gear 22 b) so that the driven gear 27 c is connectable with a rotation of the reverse shaft 18 by means of the reverse movement switching clutch 30D arranged more remote from the engine 10 than the driven gear 27 c at the reverse movement gear switching unit 20D. The reverse movement switching clutch 30D has substantially the same structure as the first switching clutch 30A except that the reverse movement switching clutch 30 D includes only an engaging member SR fixed at the driven gear 27 c, arranged at one side of the reverse movement switching clutch 30D, in an axial direction of the reverse shaft 18. When a sleeve M of the reverse movement switching clutch 30D is shifted towards the driven gear 27 c from a neutral position illustrated in FIG. 1 by means of a shift fork N, the sleeve M is spline-engaged with the engaging member SR, and the driven gear 27 c of the reverse gear set 27 is connected to the rotation of the reverse shaft 18. As a result, a reverse shift stage is established. When the sleeve M is shifted towards the back wall portion 12 a from the position where the reverse shift stage is established, the sleeve M is disengaged from the engaging member SR, and the reverse shift stage is cancelled. In this embodiment, the idler gear 27 b serves also as the driven gear 22 b of the 2nd shift stage gear set 22 a and 22 b. Alternatively, the idler gear 27 b may serve also as the driven gear 23 b of the 3rd shift stage gear set 23 a and 23 b.

In the above-described embodiment, the first forward movement gear switching unit 20A, the second forward movement gear switching unit 20B and the reverse movement gear switching unit 20D are arranged at the positions relatively close to the engine 10 within the transmission case 12, and the third forward movement gear switching unit 20C is arranged more remote from the engine 10 than the second forward movement gear switching unit 20B. The reverse movement gear switching unit 20D is arranged relatively close to the engine 10 within the transmission case 12 and includes the driving gear 27 a and the idler gear 27 b, that serve also as respective driving gear 22 a and driven gear 22 b of the 2nd shift stage gear set arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A. The 1st shift stage gear set 21 a and 21 b, arranged more remote from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b, are arranged between the driving gear 25 a of the 5th shift stage gear set 25 a, 25 b and the driving gear 26 a of the 6th shift stage gear set 26 a, 26 b, each shift stage set is arranged at each side of the third forward movement gear switching unit 20C, in the axial direction of the input shaft 15. Therefore, a rear end portion of the third forward movement gear switching unit 20C is arranged farthest from the engine 10 than rear end portions of the first forward movement gear switching unit 20A and the reverse movement gear switching unit 20D, and the rear end portion of the reverse movement gear switching unit 20D is arranged the closest to the engine 10 among the first forward movement gear switching unit 20A, the third forward movement gear switching unit 20C and the reverse movement gear switching unit 20D. Further, the first counter shaft 16, at which the driven gears 21 b and 22 b and the first switching clutch 30A of the first forward movement gear switching unit 20A are provided, is arranged above the input shaft 15 and the second counter shaft 17 at which the second forward movement gear switching unit 20B and third forward movement gear switching unit 20C are provided, as illustrated in FIG. 2. Therefore, as illustrated in FIGS. 1 and 3, the back wall portion 12 a of the transmission case 12 is formed with a first back wall portion 12 a 1, a second back wall portion 12 a 2, and a third back wall portion 12 a 3, wherein the first back wall portion 12 a 1, corresponding to the second and third forward movement gear switching units 20B and 20C, is located the farthest from the engine 10 in the back wall portion 12 a, the second back wall portion 12 a 2, corresponding to a portion of the first forward movement gear switching unit 20A provided at the first counter shaft 16, is arranged closer to the engine 10 than the first back wall portion 12 a 1, and the third back wall portion 12 a 3, corresponding to a portion of the reverse movement gear switching unit 20D provided at the reverse shaft 18, is arranged closer to the engine 10 than the second back wall portion 12 a 2. As a result, the transmission case 12 forms the stepwisely depressed cut-out portion 12 b at the upper portion of the back wall portion 12 a.

In the above-described embodiment, the transmission case 12 forms the stepwisely depressed cut-out portion 12 b at the back wall portion 12 a thereof. Hence, as illustrated in FIG. 3, in a case where the transmission 1 and the engine 10 are arranged in the axial direction thereof so as to be integrally connected with each other and then the integrally and axially connected transmission 11 and engine 10 is transversely mounted at the forward portion of the vehicle body, the upwardly curved forward portion of one of the right and left side frames 13, serving as the strength member, is arranged so as to extend through the cut-out portion 12 b of the transmission case 12. As a result, even in a case where axially connected transmission 11 and the engine 10 of the embodiment is adapted to a vehicle having side frames having the enlarged cross-sectional shapes and the linearized shapes, as illustrated in FIG. 3, one of the side frames 13 is prevented from interfering with the transmission case 12 because one of the side frames 13 extends through the cut-out portion 12 b of the transmission case 12, compared to a case where the conventional transmission 1 interferes with one of the side frames 9 a having the enlarged cross-sectional shapes and linearized shapes when the conventional transmission 1 and the engine 10 are axially connected and transversely mounted on the vehicle body, as illustrated in FIG. 6. Hence, the axially connected transmission 11 and engine 10 is transversely mountable on the vehicle body without causing interference between one of the side frames 13 and the transmission case 12.

In the above-described embodiment, the driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b, arranged at the position relatively close to the engine 10 at the first forward movement gear switching unit 20A, is fixed at the input shaft 15 and serves also as the driving gear 23 a of the 3rd shift stage gear set 23 a and 23 b, arranged at the position relatively close to the engine 10 at the second forward movement gear switching unit 20B. As a result, one of plural gears provided at the input shaft 15 is eliminated, compared to the conventional transmission apparatus. Therefore, the structure of the transmission 11 is simplified, and length of the input shaft 15 and the counter shaft 17 are shortened, which results in shortening length of the transmission case 12 in the axial direction of the input shaft 15. Further, the driving gear 27 a and the idler gear 27 b of the reverse gear set 27 serve also as respective driving gear 22 a (23 a) and the driven gear 22 b of the 2nd shift stage gear set arranged relatively close to the engine 10 at the of the first forward movement gear switching unit. Hence, even if the reverse shift stage is provided within the transmission case, a protruding amount of the transmission case 12 from the engine 10 to the first back wall portion 12 a 1 of the back wall portion 12 a is not increased.

In the above-described embodiment, the forward movement shift stage gear set, which serve also as the driving gear 27 a and the idler gear 27 b of the reverse gear set, respectively, and which is arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A, is set as the 2nd shift stage gear set, which is a gear set for low speed shift stage. Hence, a reduction gear ratio of the reverse gear set 27 is easily increased.

Further, in the transmission 11 of the above-described embodiment, the first forward movement gear switching unit 20A includes the 1st shift stage gear set 21 a, 21 b, the 2nd shift stage gear set 22 a, 22 b and the first switching clutch 30A that is provided therebetween and establishes the power transmission path established by each of the 1st shift stage gear set 21 a, 21 b and the 2nd shift stage gear set 22 a, 22 b between the input shaft 15 and the first counter shaft 16, the second forward movement gear switching unit 20B includes the 3rd shift stage gear set 23 a, 23 b, the 4th shift stage gear set 24 a, 24 b and the second switching clutch 30B that is provided therebetween and establishes the power transmission path established by each of the 3rd shift stage gear set 23 a, 23 b and the 4th shift stage gear set 24 a, 24 b between the input shaft 15 and the second counter shaft 17, and the third forward movement gear switching unit 20C includes the 5th shift stage gear set 25 a, 25 b, the 6th shift stage gear set 26 a, 26 b and the third switching clutch 30C that is provided therebetween and establishes the power transmission path established by each of the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b between the input shaft 15 and the second counter shaft 17. Accordingly, the transmission 11 is structured to have six shift stages which is a maximum number of shift stages for a transmission having three forward movement gear switching units. Hence, output torque of the transmission 11 is increased. The present invention is not limited to the above-described embodiment, but one or more of the first, second and third forward movement gear switching units 20A, 20B and 20C may include only one forward movement shift stage gear set.

In the above-described embodiment, the third forward movement gear switching unit 20C is formed with the 5th shift stage gear set (fifth forward movement shift stage gear set) 25 a, 25 b, the 6th shift stage gear set (sixth forward movement shift stage gear set) 26 a, 26 b, and the third switching clutch 30C provided therebetween. The 1st shift stage gear set (first forward movement shift stage gear set) 21 a and 21 b, arranged at the input shaft 15 so as to substantially correspond to the third switching clutch 30C in the axial direction of the input shaft 15, is positioned between the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b. The present invention is not limited to the above-described structure, but the third forward movement gear switching unit of the transmission may include only one forward movement shift stage gear set, for example, the 6th shift stage gear set 26 a and 26 b may be removed from the third forward movement gear switching unit 20C of the above-described embodiment. In the case where the third forward movement gear switching unit includes only one forward movement shift stage gear set, the 1 shift stage gear set (first forward movement shift stage gear set) 21 a and 21 b is positioned closer to the engine 10 than the 5th shift stage gear set 25 a and 25 b. As is the case with the above-described embodiment, even in the case where the third forward movement gear switching unit 20C includes only one forward movement shift stage gear set, the stepwisely depressed cut-out portion 12 b is formed at the upper back wall portion 12 a of the transmission case 12, and the effects and advantages described above are achievable.

In the above-described embodiment, the first forward movement shift stage gear set is assigned as the 1st shift stage gear set 21 a and 21 b, the second forward movement shift stage gear set is assigned as the 2nd shift stage gear set 22 a and 22 b, the third forward movement shift stage gear set is assigned as the 3rd shift stage gear set 23 a and 23 b, the fourth forward movement shift stage gear set is assigned as the 4th shift stage gear set 24 a and 24 b, the fifth forward movement shift stage gear set is assigned as the 5th shift stage gear set 25 a and 25 b, and the sixth forward movement shift stage gear set is assigned as the 6th shift stage gear set 26 a and 26 b. However, each shift stage may be assigned at any desired forward movement shift stage gear set arranged at the positions illustrated in FIGS. 1 and 2.

Further, in the above-described first and second embodiments, the case where the axially connected transmission 11 and engine 10 is adapted to the front-engine front-drive type vehicle is described above. The present invention is not limited to be adapted to the front-engine front-drive type vehicle, but the present invention is also adaptable to a rear-engine rear-drive type vehicle.

Accordingly, the first forward movement gear switching unit 20A and the second forward movement gear switching unit 20B are arranged relatively close to the engine 10 within the transmission case 12, and the third forward movement gear switching unit 20C is arranged further away from the engine 10 than the second forward movement gear switching unit 20B. The first counter shaft 16 is arranged above the input shaft 15 and the second counter shaft 17. The driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A is fixed at the input shaft 15 and serves also as the driving gear 23 a of the 3rd shift stage gear set 23 a and 23 b arranged relatively close to the engine 10 at the second forward movement gear switching unit 20B. Further, the driving gear 21 a of the 1st shift stage gear set 21 a and 21 b, arranged more remote from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b, is provided at the input shaft 15 at the position substantially corresponding to the position where the third switching clutch 30C of the third forward movement gear switching unit 20C is provided, in the axial direction of the input shaft 15. The reverse gear set 27 includes the driving gear 27 a provided at the input shaft 15, the driven gear 27 c rotatably supported at the reverse shaft 18 and connected to the rotation of the reverse shaft 18 by means of the reverse movement switching clutch 30D, and the idler gear 27 b rotatably supported at the first counter shaft 16 or the second counter shaft 17 and engaging with the driving gear 27 a and the driven gear 27 c. The driving gear 27 a and the idler gear 27 b of the reverse gear set 27 serve also as the respective 2nd shift stage gear set 22 a and 22 b arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A or the respective 3rd shift stage gear set 23 a and 23 b arranged relatively close to the engine 10 at the second forward movement gear switching unit 20B. As a result, the transmission case 12, located at the opposite side of the engine 10, is formed to have the first back wall portion 12 a 1 corresponding to the second and third forward movement gear switching units 20A and 20B, the second back wall portion 12 a 2 corresponding to the portion of the first forward movement gear switching unit 20A, and the third back wall portion 12 a 3 corresponding to the portion of the reverse movement gear switching unit 20D, wherein the second back wall portion 12 a 2 is located closer to the engine 10 than the first back wall portion 12 a 1 arranged below the second back wall portion 12 a 2 and wherein the third back wall portion 12 a 3 is located closer to the engine 10 than the second back wall portion 12 a 1 arranged below the third back wall portion 12 a 3, thereby creating the cut-out portion 12 b at the upper portion of the back wall 12 a. By adapting the above-structured transmission 11, the transmission 11 and the engine 10 are connected in the axial direction thereof, and then the axially connected transmission 11 and engine 10 is transversely mounted on the vehicle body so that one of the side frames 13, extending along the both sides of the vehicle body in the front-rear direction thereof, extends through the cut-out portion 12 b of the transmission case 12. Therefore, even in a case where axially connected transmission 11 and the engine 10 of the embodiment is adapted to a vehicle having side frames having the enlarged cross-sectional shapes and linearized shapes, as illustrated in FIG. 3, one of the side frames 13 is prevented from interfering with the transmission case 12 because the one of the side frames 13 extends through the cut-out portion 12 b of the transmission case 12, compared to a case where the conventional transmission 1 interfered with one of the side frames 9 a having the enlarged cross-sectional shapes and linearized shapes when the conventional transmission 1 and the engine 10 are axially connected and transversely mounted on the vehicle body, as illustrated in FIG. 5. Hence, the axially connected transmission 11 and engine 10 is transversely mountable on the vehicle body without causing interference between one of the side frames 13 and the transmission case 12. As a result, the transmission 11 of the embodiment is reduced in weight by forming sufficient space at outside of the upper portion of the back wall portion 12 a of the transmission case 12 by arranging the second back wall portion 12 a 2 to be closer to the engine 10 than the first back wall portion 12 a 1 and arranging the third back wall portion 12 a 3 to be further closer to the engine 10 than the second back wall portion 12 a 2. By forming the stepwisely depressed cut-out portion 12 b at the upper portion of the back wall portion 12 a of the transmission case 12, mountability of the transmission 11 of the embodiment is increased, i.e. the transmission 11 of the embodiment is adapted to vehicles having various shapes of the side frames 13. Further, as the driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b, arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A, serves also as the driving gear 23 a of the 3rd shift stage gear set 23 a and 23 b, arranged relatively close to the engine 10 at the second forward movement gear switching unit 20B, one of the plural driving gears is eliminated. Moreover, as the driving gear 21 a of the 1st shift stage gear set 21 a and 21 b, arranged more remote from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b, is provided at the input shaft 15 at the position substantially corresponding to the position where the third switching clutch 30C of the third forward movement gear switching unit 20C is provided, in the axial direction of the input shaft 15, the lengths of the second and third forward movement gear switching units 20B and 20C, which are arranged in parallel to each other in the axial direction of the input shaft 15, are not elongated. As a result, the structure of the transmission 11 is simplified and the transmission 11 is downsized. Further, the driving gear 27 a and the idler gear 27 c of the reverse gear set 27 serve also as the respective 2nd shift stage gear set 22 a and 22 b arranged relatively close to the engine 10 at the second forward movement gear switching unit 20B. Hence, even if the reverse gear set 27 is provided within the transmission case 12, the protruding amount from the engine 10 to the first back wall portion 12 a 1 is not increased.

According to the embodiment, the 2nd forward shift stage gear set 22 a and 22 b arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A serving also as the driving gear 27 a and the idler gear 27 b, respectively, of the reverse gear set 27, or the 3rd forward movement shift stage set 23 a and 23 b arrange relatively close to the engine 10 at the second forward movement gear switching unit 20B serving also as the driving gear 27 a and the idler gear 27 b, respectively, of the reverse gear set 27, is set as a gear set for a low speed shift stage.

Accordingly, the 2nd shift stage gear set 22 a and 22 b arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A, serving also as the respective driving gear 27 a and the idler gear 27 b of the reverse gear set 27, is set as a low speed shift stage. Alternatively, the 3rd shift stage gear set 23 a and 23 b arranged relatively close to the engine 10 at the second forward movement gear switching unit 20B, serving also as the respective driving gear 27 a and the idler gear 27 b of the reverse gear set 27, is set as a low speed shift stage. Hence, the reduction gear ratio of the reverse gear set 27 is easily set larger.

According to the embodiment, the first forward movement gear switching unit 20A includes the 1st shift stage gear set 21 a, 21 b, the 2nd shift stage gear set 22 a, 22 b and the first switching clutch 30A arranged therebetween and establishing the power transmission path established by each of the 1st shift stage gear set 21 a, 2 1 b and the 2nd shift stage gear set 22 a, 22 b between the input shaft 15 and the first counter shaft 16, the second forward movement gear switching unit 20B includes the 3rd shift stage gear set 23 a, 23 b, the 4th shift stage gear set 24 a, 24 b and the second switching clutch 30B arranged therebetween and establishing the power transmission path established by each of the 3rd shift stage gear set 23 a, 23 b and the 4th shift stage gear set 24 a, 24 b between the input shaft 15 and the second counter shaft 17, and the third forward movement gear switching unit 20C includes the 5th shift stage gear set 25 a, 25 b, the 6th shift stage gear set 26 a, 26 b and the third switching clutch 30C arranged therebetween and establishing the power transmission path established by each of the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b between the input shaft 15 and the second counter shaft 17.

Accordingly, the first forward movement gear switching unit 20A includes the 1st shift stage gear set 21 a, 21 b, the 2nd shift stage gear set 22 a, 22 b, and the first switching clutch 30A that is provided therebetween and establishes the power transmission path established by each of the 1st shift stage gear set 21 a, 21 b and 2nd shift stage gear set 22 a, 22 b between the input shaft 15 and the first counter shaft 16. The second forward movement gear switching unit 20B includes the 3rd shift stage gear set 23 a, 23 b, the 4th shift stage gear set 24 a, 24 b, and the second switching clutch 30B that is provided therebetween and establishes the power transmission path established by each of the 3rd shift stage gear set 23 a, 23 b and the 4th shift stage gear set 24 a, 24 b between the input shaft 15 and the second counter shaft 17. The third forward movement gear switching unit 20C includes the 5th shift stage gear set 25 a, 25 b, the 6th shift stage gear set 26 a, 26 b, and the third switching clutch 30C that is provided therebetween and establishes the power transmission path established by each of the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b between the input shaft 15 and the second counter shaft 17. Accordingly, the transmission 11 has the six shift stages, which is the maximum number of shift stages for a transmission having three forward movement gear switching units. Hence, the output torque of the transmission 11 is increased.

The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the sprit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby. 

1. A vehicle comprising: an engine; a pair of side frames provided at the vehicle so as to extend along both sides of a vehicle body in a front-rear direction of the vehicle; and a transmission adapted to be axially connected with the engine and adapted to be transversely mounted on the vehicle body, including: an input shaft adapted to be rotatably driven by the engine; an output shaft adapted to be connected to driving wheels; a first counter shaft arranged in parallel to the input shaft and connected to the output shaft; a second counter shaft arranged in parallel to the input shaft and connected to the output shaft; a reverse shaft arranged in parallel to the input shaft and connected to the output shaft; a first gear mechanism between the input shaft and the first counter shaft, the first gear mechanism having a first gear set, a second gear set and a first switching clutch therebetween to selectively establish power transmission paths between the input shaft and the first counter shaft; a second gear mechanism between the input shaft and the second counter shaft, the second gear mechanism having a third forward movement shift stage gear set, optionally a fourth forward gear set and a second switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the third gear set or, if present, the fourth gear set; a third gear mechanism between the input shaft and the second counter shaft, the second and third gear mechanisms extending in parallel with one another between the input shaft and second counter shaft, the third gear mechanism having a fifth gear set, optionally a sixth gear set and a third switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the fifth gear set or, if present, the sixth gear set; a reverse movement gear switching mechanism having a reverse gear set provided between the input shaft and the reverse shaft and a reverse movement switching clutch for selectively establishing a power transmission path between the input shaft and the reverse shaft via the reverse gear set; and a transmission case supporting and covering most of the input shaft, the first counter shaft, the second counter shaft, the reverse shaft, the output shaft, the first gear mechanism, the second gear mechanism, the third gear mechanism and the reverse movement gear switching mechanism; wherein the first gear mechanism and the second gear mechanism are arranged relatively close to the engine, the third gear mechanism is arranged at a position more remote from the engine than the second gear mechanism, and the first counter shaft is arranged above both the input shaft and the second counter shaft, a driving gear of the second gear set, which is arranged closer to the engine than a driving gear of the first gear set of the first gear mechanism, serves also as a driving gear of the third gear set and is arranged closer to the engine than a driving gear of the fourth gear set of the second gear mechanism, and a driving gear of the first gear set, which is arranged farther from the engine than the driving gear of the second hear set of the first gear mechanism, is positioned substantially aligned with the third switching clutch, in the axial direction of the input shaft, the reverse gear set includes a driving gear provided at the input shaft, a driven gear rotatably supported at the reverse shaft and rotatably connectable to the reverse shaft by means of the reverse movement switching clutch, and an idler gear rotatably supported at the first counter shaft and engaging with the driving gear and the driven gear of the reverse gear set, wherein the driving gear of the reverse gear set serve also as the driving gear for the second gear set, and wherein the transmission case includes a back wall portion formed with a first back wall portion corresponding to the second forward movement gear switching unit and the third forward movement gear switching unit, a second back wall portion corresponding to the first gear mechanism and located closer to the engine than the first back wall portion, and a third back wall portion corresponding to a portion of the reverse movement gear switching mechanism provided at the reverse shaft and located even closer to the engine than the second back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion, and wherein the transmission is axially connected to the engine and transversely mounted on the vehicle body so that one of the side frames extending along the both sides of the vehicle body in the front-rear direction thereof extends through the cut-out portion.
 2. The vehicle according to claim 1, wherein the second gear set arranged relatively close to the engine at the first gear mechanism serves also as the driving gear and the idler gear, respectively, of the reverse gear set, and is set as a gear set for a low speed shift stage.
 3. The vehicle according to claim 1, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the first counter shaft via each of the first gear set and the second gear set, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the second counter shaft via each of the third gear set and the fourth gear set, and the third gear mechanism includes the fifth gear set, the sixth gear set and the third switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the second counter shaft via each of the fifth gear set and the sixth gear set.
 4. The vehicle according to claim 2, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the first counter shaft via each of the first gear set and the second gear set, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the second counter shaft via each of the third gear set and the fourth gear set, and the third gear mechanism includes the fifth gear set, the sixth gear set and the third switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the second counter shaft via each of the fifth gear set and the sixth gear set.
 5. A transmission adapted to be axially connected with an engine and adapted to be transversely mounted on a vehicle body, comprising: an input shaft adapted to be rotatably driven by the engine; an output shaft adapted to be connected to driving wheels; a first counter shaft arranged in parallel to the input shaft and connected to the output shaft; a second counter shaft arranged in parallel to the input shaft and connected to the output shaft; a reverse shaft arranged in parallel to the input shaft and connected to the output shaft; a first gear mechanism between the input shaft and the first counter shaft, the first gear mechanism having a first gear set, a second gear set and a first switching clutch therebetween to selectively establish power transmission paths between the input shaft and the first counter shaft; a second gear mechanism between the input shaft and the second counter shaft, the second gear mechanism having a third gear set, optionally a fourth gear set and a second switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the third gear set or, if present, the fourth gear set; a third gear mechanism between the input shaft and the second counter shaft, the second and third gear mechanisms extending in parallel with one another between the input shaft and the second counter shaft, the third gear mechanism having a fifth gear set, optionally a sixth gear set and a third switching clutch for selectively establishing a power transmission path between the input shaft and the second counter shaft via the fifth gear set or, if present, the sixth gear set; a reverse movement gear mechanism having a reverse gear set provided between the input shaft and the reverse shaft and a reverse movement switching clutch for selectively establishing a power transmission path between the input shaft and the reverse shaft via the reverse gear set; and a transmission case supporting and covering most of the input shaft, the first counter shaft, the second counter shaft, the reverse shaft, the output shaft, the first gear mechanism, the second gear mechanism, the third gear mechanism and the reverse movement gear mechanism; wherein the first gear mechanism and the second gear mechanism are arranged relatively close to the engine, the third gear mechanism is arranged at a position more remote from the engine than the second gear mechanism, and the first counter shaft is arranged above both the input shaft and the second counter shaft, a driving gear of the second gear set, which is arranged closer to the engine than a driving gear of the first gear set of the first gear mechanism, serves also as a driving gear of the third gear set and is arranged closer to the engine than a driving gear of the fourth gear set of the second gear mechanism, and a driving gear of the first gear set, which is arranged farther from the engine than the driving gear of the second gear set of the first gear mechanism, is positioned on the input shaft substantially aligned with the third switching clutch, in the axial direction of the input shaft, the reverse gear set includes a driving gear provided at the input shaft, a driven gear rotatably supported at the reverse shaft and rotatably connectable to the reverse shaft by means of the reverse movement switching clutch, and an idler gear rotatably supported at the first counter shaft or the second counter shaft and engaging with the driving gear and the driven gear of the reverse gear set, wherein the driving gear of the reverse gear set serve also as the driving gear for the second gear set, and wherein the transmission case includes a back wall portion formed with a first back wall portion corresponding to the second forward movement gear switching unit and the third forward movement gear switching unit, a second back wall portion corresponding to the first gear mechanism and located closer to the engine than the first back wall portion, and a third back wall portion corresponding to a portion of the reverse movement gear mechanism provided at the reverse shaft and located even closer to the engine than the second back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion.
 6. The transmission according to claim 5, wherein the second gear set arranged relatively close to the engine at the first gear mechanism serves also as the driving gear and the idler gear, respectively, of the reverse gear set, or the third stage set arrange relatively close to the engine at the second gear mechanism serves also as the driving gear and the idler gear, respectively, of the reverse gear set, and is set as a gear set for a low speed shift stage.
 7. The transmission according to claim 5, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the first counter shaft via each of the first gear set and the second gear set, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the second counter shaft each of the third gear set and the fourth gear set, and the third gear mechanism includes the fifth gear set, the sixth gear set and the third switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the second counter shaft via each of the fifth gear set and the sixth gear set.
 8. The transmission according to claim 6, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the first counter shaft via each of the first gear set and the second gear set, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the second counter shaft each of the third gear set and the fourth gear set, and the third gear mechanism includes the fifth gear set, the sixth gear set and the third switching clutch arranged therebetween for selectively establishing power transmission paths between the input shaft and the second counter shaft via each of the fifth gear set and the sixth gear set. 